Field of the Invention
The present invention relates to a semiconductor memory device, especially regarding compression, extension or error correction of input/output data.
Description of the Related Art
Since the circuit density of the semiconductor memory such as flash memories or dynamic random access memories (DRAMs) has increased year by year, it has become difficult to manufacture without faulty or defective products. Therefore, regarding the memory chip, a long scheme is needed to detect and compensate for the physical defects of the memory devices occurred in the manufacturing process. For example, long schemes are utilized to compensate the memory chip with physical defects when the large memory is arranged. In addition to the physical compensation of the large memory, the semiconductor memory also includes the error-checking correction (ECC) circuit which corresponds to the software error.
Regarding the NAND-type flash memory, because the programming or erasing is repeatedly performed on the data, the degradation of the tunnel insulation layer results in the degradation of the charge-maintaining ability, and the charges trapped by the tunnel insulation layer results in the variation of the threshold value which causes the bit error. Patent document 1 corresponds to the above bit error and arranges an ECC circuit. It should be noted that due to photolithography, the patterns of the cells near the group selection transistor are not uniform. Since the ion injection is not uniform when the diffusion layer is formed, the bit error increases. Therefore, an ECC code is arranged to execute further compensation.
In addition, Patent document 2 provides a semiconductor device equipped with an error corrector. The error corrector is arranged to perform the error correction on the input data input to the NAND flash memory or the output data from the NAND flash memory. Within the semiconductor device, the connection between the NAND flash memory and the error corrector is adjustable to decrease the area of the circuit.